The present invention relates generally to sonar equipment for underwater generation of sound and more particularly to the structure of an electromagnetic drive system for a sound transducer or projector having piston means for generating acoustic waves and including pressure compensation means.
In the technology of underwater sound generating equipment, three design parameters are of compelling importance. These are weight, volume and power. In many applications, the ability to maintain power or reduce volume while reducing or limiting weight is of significant importance.
In moving coil transducers, electromagnetic means including a moving coil operate to drive piston means which produce the energy. The type of electromagnetic arrangement utilized can have a significant affect upon power output and overall weight.
The development of rare earth permanent magnet materials provided opportunities to improve the designs and performance of devices, such as underwater sound transducers, which relied upon the previous generation of magnetic materials; generally ferrites and Alnico alloys.
Among such devices are the electrodynamic or "moving-coil" transducers. A typical electrodynamic transducer is the loudspeaker. However, the high cost of the new rare earth materials and the relatively satisfactory performance of existing ferrite materials provided little incentive for such applications. However, a related device, the electrodynamic sonar transducer, had much to gain.
In prior art devices, the substantial increases in magnetic flux made available by the new material for a given magnet assembly volume and weight were a welcome development because of the already high costs associated with the construction of each sonar unit. However, since increased flux density requires iron pole pieces adequate to carry this magnetic flux from the permanent magnet assembly to the air gap and return, the weight associated with the iron pole pieces can produce problems in certain applications. Thus, reducing the amount of iron required for the pole pieces without reducing the power delivered by the electromagnetic drive means can provide a significant advantage, particularly in underwater transducers where weight is an important consideration.
Accordingly, it is an object of the present invention, to provide an improved electromagnetic drive arrangement for a moving coil transducer which provides enhanced power characteristics without creating the need for increasing the weight of the iron pole pieces. Because of the particular arrangement of the permanent magnet members of the electromagnetic drive means in accordance with the present invention, pole piece weight may be reduced without decreasing power output or, conversely, power may be increased without increasing the iron required for the pole pieces, as would ordinarily be necessary with prior art devices.